1. Field of the Invention
The present invention relates to activated carbon materials suitable for the use in treatments for the decomposition of various compounds contained in waste water such as waste water withdrawn, for instance, from chemical plants, from semiconductor treatment plants, from metal surface treatment plants, etc. The active carbon materials are useful, for example, as catalysts for the decomposition of hydrogen peroxide, hydrazines or water pollutants such as quaternary ammonium salts, organic acids, sulfur-containing compounds and the like.
2. Related Art
At present, hydrogen peroxide is commercially produced on a large scale, and used in various industrial fields, for instance, as a bleaching agent for paper pulps and fibers, as fungicide and oxidizing agent for medical use, as a bleaching agent for foodstuffs, as agent for metal surface treatments and, as a cleaning agent for semiconductors.
However, if a hydrogen peroxide-containing waste water is directly poured into an ordinary waste water treatment tank or the like without any operations for the decomposition of hydrogen peroxide, then the hydrogen peroxide-containing waste water may cause an undesired increase of COD. Furthermore, when a hydrogen peroxide-containing waste water enters an apparatus for carrying out biologically activated sludge process, then the hydrogen peroxide is decomposed to generate gaseous oxygen, which will cause a flowing of suspensions in a sedimentation tank, so that there may be a undesired lowering of quality of refined water obtained by the water treatment.
Thus, hydrogen peroxide may cause various problems in waste water treatments. Therefore, hydrogen peroxide in a waste water is usually subjected to a treatment for the decomposition thereof before the waste water is discarded.
It is known that there are a number of methods for the decomposition of hydrogen peroxide, including (1) a decomposition method comprising the use of chemicals such as sodium bisulfite, (2) a decomposition method comprising the use of manganese dioxide as catalyst, (3) a decomposition method comprising the use of activated carbon, (4) a decomposition method comprising the use of enzymes such as catalase and the like.
However, in the method (1), the decomposition reaction results in evolution of gaseous sulfur dioxide, which causes an environmental pollution. In addition, it is necessary to use sodium bisulfite or the like in an amount twice as much as the stoichiometric amount based on the amount of hydrogen peroxide, and therefore the use of such a large amount of sodium bisulfite will result in an increase of operation costs. Furthermore, the excess sodium bisulfite may cause an increase of COD and hence a secondary environmental pollution. In the method (2), there is a leaching of manganese during the decomposition reaction. Particularly, there is a violent leaching of manganese under acidic conditions, and therefore an environmental pollution is caused by manganese. The methods (3) generally has a low decomposition activity, and also has such a drawback that the effective life of the catalysts is rather short. The method (4) employs enzymes such as catalase, so that the pH of the reaction solution is limited to a neutral range, and that the reaction operation must be carried out at room temperature. Thus, these known methods have many problems, and therefore it is desirable to provide an improved method.
At present, hydrazine and salts and derivatives thereof, which are hereinafter referred to as "hydrazine(s)", are widely used as boiler water treating chemicals, reductants, agricultural chemicals, polymerization catalysts, foaming agents, agents for treating semiconductors, agents for water treatments and the like. In the case of the treatment of a hydrazine-containing waster water, an operation is conducted at the first time for the decomposition of hydrazines. A prior method for the decomposition of hydrazines comprises adding sodium hypochlorite to a hydrazine-containing waste water to effect an oxidative decomposition of hydrazines. The oxidative decomposition of hydrazine may be showed by the following reaction formula: EQU N.sub.2 H.sub.4 +4NaOCl.fwdarw.2H.sub.2 O+N.sub.2 +O.sub.2.
In this reaction, use is made of a large amount of sodium hypochlorite, so that a high expense is necessary for this operation. In addition, there is a drawback that, after the oxidative decomposition treatment, a small amount of chlorine remains in the waste water.
Japanese Patent Applications (KOKAI) Nos. 91093/1978 and 91095/1978 disclose a method, wherein hydrazines are decomposed with air in the presence of heavy metals as catalysts. The decomposition of hydrazine with air may be shown by the reaction formula: EQU N.sub.2 H.sub.4 +O.sub.2 .fwdarw.N.sub.2 +2H.sub.2 O.
However, in this method, the decomposition velocity is low, and the decomposition of hydrazines is insufficient. Furthermore, there may be a secondary environmental pollution caused by the heavy metals. So, the known method cannot be regarded as an industrially useful method.
Furthermore, water pollution has increased in recent years with industrial development and exerts a great influence on the natural environment in rivers, lakes and seas. It is known that there are many methods or processes and much equipment for the treatment of waste water including other water pollutants described above. For example, such methods as biological treatment by activated sludge, methods of adsorption by activated carbon, methods of oxidation by ozone, and "Fenton" methods which effect oxidation using iron salts with such oxidants as hydrogen peroxide.
However, problems concerning these methods include the necessity, in methods which use activated sludge, of a large area for facilities and long treatment time as well as limitations on the kinds of organic compounds in the water pollutants. In adsorption methods, the volume of water pollutants that can be adsorbed is small, so a large amount of adsorbent is necessary, and the removal of the adsorbed pollutant is very complicated. Methods of decomposition by ozone are very expensive due to the high cost of equipment necessary for the production of ozone.
Treatment by the "Fenton" method, is a decomposition method which uses the oxidative ability of an oxidant (usually hydrogen peroxide) in the presence of iron salts, and since it is necessary to use more than one equivalent of iron (ferrous) ion per one equivalent of hydrogen peroxide, the volume of iron salt used is very large. The ferric ion produced by the treatment, after neutralization using a base, is precipitated using a polymer flocculant and is then recovered as sludge. For this reason, a large volume of sludge is produced and treatment of sludge becomes necessary as well. Also, to the extent that a large amount of iron ion is used, it is also necessary to use a large volume of such chemicals as base and polymer flocculants. This causes such problems as high treatment costs. Additionally, in this method, if any hydrogen peroxide remains after treatment, the hydrogen peroxide itself becomes a factor in the increase of COD and has a negative effect upon the environment. Consequently, remaining hydrogen peroxide must be removed and this again creates the necessity of adding a large amount of iron (ferrous) ion which causes the amount of chemicals used and the amount of sludge produced to increase. In addition, the kinds of organic compounds in water pollutants which can be treated is very limited as well.
There are various problems in the prior art hydrogen peroxide, hydrazine or other water pollutant decomposition methods described above. The present invention provides a novel catalyst for the decomposition of hydrogen peroxide, hydrazine and other water pollutants which comprises activated carbon materials which can cause decomposition with no risk of secondary environmental pollution and which can be used in a broad pH range and exhibits high activity for the decomposition of hydrogen peroxide and hydrazine, and additionally, which causes the decomposition a wide range of water pollutants in a short time under mild conditions.